1. Field of the Invention
The present invention relates to a construction, a surface emitting laser, and a light-emitting device having the surface emitting laser.
2. Description of the Related Art
Surface emitting lasers which emit a laser beam in a direction perpendicular to the semiconductor substrate surface are being studied and developed actively. The surface emitting laser gives a stable single vertical mode and facilitates two-dimensional arraying. Therefore, the surface emitting laser is promising as a light source for optical communication and optical transmission, and a light source for electrophotography.
A surface emitting laser employing a two-dimensional photonic crystal is disclosed in Japanese Patent Application Laid-Open No. 2003-273453. The photonic crystal is a structure which has the refractive index changing periodically in a repeating distance nearly equal to or shorter than the light wavelength. The two-dimensional photonic crystal surface emitting laser disclosed in Japanese Patent Application Laid-Open No. 2003-273453 comprises an active layer which emits light on injection of a carrier, and a photonic crystal periodic structure which has a two-dimensional refractive index cycle, adjacently to the active layer. The photonic crystal is formed by inscription in a slab-shaped waveguide having a higher refractive index placed horizontally on a substrate, and emits light in the direction perpendicular to the substrate by resonance of the light enclosed in the slab-shaped waveguide.
U.S. Pat. No. 6,154,480 discloses a surface emitting laser which employs a slab containing a photonic crystal as a resonator mirror by utilizing guided mode resonance (hereinafter referred to as “GMR”). In this surface emitting laser, the waveguide mode in the slab waveguide resonates with the radiation mode for emitting the light from the slab by the photonic crystal formed in the slab waveguide. Thereby, the photonic crystal-containing slab is capable of decreasing the transmittance or increasing the reflectivity remarkably of the incident light in a direction perpendicular to the face of the slab wave guide at the GMR resonance wavelength. That is, the photonic crystal-containing slab serves as a mirror.
However, the above-mentioned two-dimensional photonic crystal surface emitting laser has disadvantages below.
The technique disclosed in Japanese Patent Application Laid-Open No. 2003-273453 causes loss of light by leakage through the non-photonic region of the slab not containing the photonic crystal structure (hereinafter referred to as a “non-photonic structure region”) to lower the light utilization efficiency. In a practical device, since the size of region containing the photonic crystal structure (hereinafter referred to as a “photonic structure region”) is limited, a part of the light resonating in the photonic structure region propagates in the waveguide and leaks out of the photonic structure region. The light leaking to the non-photonic structure region does not contribute the laser oscillation, and cannot be utilized as the surface emission output to cause a loss of light and to lower the light utilization efficiency.
In the laser described in U.S. Pat. No. 6,154,480 also, since the size of the photonic structure region is limited, a part of the light resonating by GMR in the photonic crystal slab leaks out in the direction of plane of slab waveguide. As the result, the reflectivity of the mirror utilizing the GMR is decreased corresponding to the leakage to decrease the output of the surface emitting laser employing the above mirror.
Incidentally, the laser described in Japanese Patent Application Laid-Open No. 2003-273453 is classified as a distributed feed back laser type (DFB type), and the laser described in U.S. Pat. No. 6,154,480 is classified as a vertical cavity surface emitting laser type (VCSEL type).
The present invention intends to provide a construction, a surface emitting laser which enables effective utilization of the leaking light guided in the horizontal direction of the slab containing the photonic crystal, and to provide a light emitting device having the surface emitting laser.